Which sentence correctly uses commas to set off a nonrestrictive clause?

• A. The scientist, who won the award, spoke tonight.
• B. The scientist who won the award spoke tonight.
• C. The scientist, who won the award spoke tonight.
• D. The scientist who won, the award spoke tonight.

Answer: (A)

Setting off a nonrestrictive clause with commas is the key idea here. A nonrestrictive clause adds extra information about a noun that’s already identified and can be removed without changing which noun you’re talking about. It’s like a aside that doesn’t limit the meaning.

In the correct sentence, the clause who won the award is enclosed by commas: The scientist, who won the award, spoke tonight. You can take out the middle bit and still have a complete, clear sentence: The scientist spoke tonight. The commas signal that this extra information is optional and not needed to identify which scientist is being discussed.

The other options don’t follow this rule. Without commas, The scientist who won the award spoke tonight uses a restrictive clause, narrowing which scientist is meant to imply that only the scientist who won the award spoke tonight. That’s not the intended nonrestrictive usage. If there’s a comma only before the clause but not after, as in The scientist, who won the award spoke tonight, the sentence isn’t properly punctuated to enclose the nonrestrictive clause. And The scientist who won, the award spoke tonight breaks the sentence structure entirely, making it incorrect and nonsensical.